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Old 10-10-2022, 08:43 PM   #1
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2003 Big Sky Batteries wonít charge on shore power

We have a 2003 Montana Big Sky. My battery will not charge when attached to 50amp shore power.
I have to keep a trickle charger on the battery all the time or it will go dead quickly. I have removed the wall in the cargo basement exposing the back of the electrical panel. There are no visible fuses, only wires exiting the metal box.
All fuses and breakers are in working order inside the RV behind the panel. What am I looking for or doing wrong?
Thanks in advance.
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Old 10-10-2022, 08:49 PM   #2
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The disconnect key in your wet by will need to be in such a position that it can not be removed. That will place it in the On position for 12VDC to the battery. If you have already configured in this position, then the converter for a 2003 model may have gone out and not be outputting 12VDC to charge your batteries with.

Edit: Just realized this was your first post. Welcome to the MOC family! Lots of helpful folks on here. I'm sure others will chime in with other suggestions as well.
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Old 10-10-2022, 08:54 PM   #3
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Thanks for the warm welcome. I do not have any disconnect key of any kind in the wet bay or anywhere that I can see.
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Old 10-10-2022, 09:30 PM   #4
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Below is a diagnostic approach for newer Montanas. Much of it applies to your older model. The two major differences are: you don't have a disconnect switch in the Convenience Center (as you don't have that either); and you converter is likely a stand alone unit located near the converter but not integrated into it.
The 12V flow from the converter to the batteries is pretty straight forward. As others have pointed out, here are the places to look. All connections should have 13.5 +/- Volts if the converter is working.

  • The converter is part of the power distribution panel -Ensure the CB for it is On
  • There are Reverse Polarity Fuses on the converter which protect against connecting a battery backwards. - Ensure they are not blown.
  • Check the output voltage at the converter. - it should be in the 13.5V DC range.
  • The power then runs to the Disconnect Switch in the Convenience Center. - Ensure the Red Key is in the position where it can *NOT* be removed. If removed, this interrupts the power charging the battery. The Disconnect Switch is not know to fail, but you can remove it to check there is power in and out of it just to be sure.
  • The power next flows to the group of 50 amp self-resetting CBs behind the battery. We all know about the one that hiccups and interrupts the hydraulic system. That one also passes power to/from the converter and batteries. You want to check it and it's brother (it is in the current flow to the battery) to ensure there is 13.5V on *EACH* side of the CB.
  • The last connection is the one from the 50 amp CBs to the batteries. Ensure you have clean connections and the cables are not corroded (watch out for internal corrosion under the shrink wrap).
Somewhere along this path there will be the problem. A simple VOM should find it. I hope this helps.
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Old 10-11-2022, 07:09 PM   #5
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How old is the battery....if mentioned, I missed it? If OEM, that explains it.
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battery charging, converter, electrical

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